Washington ? Wisconsin’s blue-collar and liberal traditions run through American pop culture and politics. When the state that gave us Cheeseheads, “Laverne & Shirley” and political progressives holds its presidential primary Tuesday, the results could help determine whether Hillary Rodham Clinton or Barack Obama gets the Democratic nomination.

Clinton led there by 9 points early this month, according to one major survey, but two more recent polls show Obama now with a small lead.

Even if Wisconsin turns into a blowout, their rivalry almost certainly will endure through bigger primaries March 4 in Texas and Ohio. Nevertheless, Wisconsin’s often historic role in shaping past presidential elections makes it a state worth watching.

President Lyndon Johnson dropped his re-election bid in 1968 when he realized that he was poised to lose Wisconsin’s Democratic primary to Gene McCarthy.

Eight years earlier, John F. Kennedy’s win in the state’s primary over next-door-neighbor Hubert H. Humphrey of Minnesota helped establish the credibility of his national appeal. In 1992, Wisconsin Democrats narrowly chose Bill Clinton over California’s Jerry Brown, pointing the way for the national party’s ultimate choice.

In general elections, the nation’s 18th-largest state, with about 5.6 million residents, also has been a battleground. It chose Democrat John Kerry over President Bush by only 50-49 percent in 2004, and Democrat Al Gore over Bush by about 5,000 votes in 2000.

Clinton and Obama each have constituencies in the state, said Barry Burden, a professor of political science at University of Wisconsin, Madison.

“It’s a lot of working-class whites without college educations, who are social moderates and responsible Midwesterners,” Burden said. Manufacturing makes up more than one-fourth of the state’s industry. These voters are a core part of Clinton’s constituency.

At the same time, Burden said, “you do have that progressive, reformist element, and I think the anti-war element is tied up in that.” That profile fits key parts of Obama’s coalition.

Two polls taken since Feb. 8 put Obama ahead of Clinton, but only by 4 percentage points, at or near the surveys’ statistical margins of error. While that isn’t much of a lead, Clinton had led by 9 points on Feb. 6-7, according to an American Research Group poll released Feb. 8, so the trend is clear.

What seems to have pushed Obama ahead in Wisconsin is not his more liberal reputation, Burden said, but “the energy coming off of the other states” where he’s beaten Clinton in eight straight contests starting Feb. 9.